Chapter 14 review
1
For the overall hypothetical reaction A + 5B → 4C, the rate of appearance of C given
by Δ[C]/Δt is the same as
A) Δ[A]/Δt
B) -(5/4)(Δ[B]/Δt)
C) -(4/5)(Δ[B]/Δt)
D) -(1/4)(Δ[A]/Δt)
E) none of the above.
2
When heated, the compound RX3 decomposes to a mixture of products. The following
data were collected for the decomposition at 100º C. What is the average rate of
reaction, -Δ [RX3]/Δt, over the entire experiment?
A)
B)
C)
D)
E)
0.0028 mol/L.s
0.045 mol/L.s
0.0014 mol/L.s
-0.0027 mol/L.s
0.0057 mol/L.s
3
The initial rate of the reaction PCl5 → PCl3 + Cl2 is increased a factor of four when
the concentration of PCl5is doubled. Therefore, the rate
A) depends on the concentrations of PCl3 and Cl2.
B) is first order with respect to PCl5.
C) is second order with respect to PCl5.
D) is fourth order with respect to PCl5.
E) is first order with respect to PCl3.
4
Bromine atoms react with iso-butane (iso-C4H10) to form hydrogen bromide and the tbutyl radical (t-C4H9): Br + iso-C4H10 → HBr + t-C4H9. The reaction is first order
with respect to each of the reactants, and at 298 K, the rate constant is 1.02 x 106 L
mol-1 s-1. Calculate the initial rate of the reaction in a 4.0 L reaction vessel containing
0.60 moles of iso-butane and 0.00010 moles of bromine atoms.
A) 1.5 mol L-1 s-1
B) 3.8 mol L-1 s-1
C) 2.5 x 1011 mol L-1 s-1
D) 2.5 x 102 mol L-1 s-1
E) 6.7 x 102 mol L-1 s-1
1
5
Consider the thermal decomposition of cyclobutane (C4H8(g)) at 438º C, C4H8(g) →
2C2H4(g). The reaction follows first-order kinetics and the rate constant is k = 2.48 x
10-4 s-1. If the initial concentration of cyclobutane is 0.800 mol/L, what concentration
will remain after 10.0 min?
A) 0.689 mol/L
B) 0.455 mol/L
C) 0.333 mol/L
D) 0.248 mol/L
E) 0.0061 mol/L
6
A certain first-order reaction is 46 % complete in 68 min at 25°C. What is its rate
constant?
A) 9.1 x 10-3 min-1
B) 1.1 x 10-2 min-1
C) 31 min-1
D) 51 min-1
E) none of the above
7
Consider the reaction A → products. Which, if any, of the following plots is
consistent with a second-order reaction?
A) ln[A] plotted against time gives a straight line of positive slope.
B) ln[A] plotted against time gives a straight line of negative slope.
C) 1/[A] plotted against time gives a straight line of positive slope.
D) 1/[A] plotted against time gives a straight line of negative slope.
E) None of the above plots is consistent with a second-order reaction.
8
Consider the reaction A → products. Which of the following plots is consistent with a
zero-order reaction?
A) [A] plotted against time gives a horizontal, straight line.
B) ln[A] plotted against time gives a straight line of negative slope.
C) 1/[A] plotted against time gives a straight line of positive slope.
D) [A] plotted against time gives a straight line of negative slope.
E) [A] plotted against time gives a curved line of negative slope, decreasing in
magnitude as time increases.
9
What is the value of the rate constant for a first-order reaction for which the half-life
is 26.7 min?
A) 18.5 min-1
B) 38.5 min-1
C) 9.25 min-1
D) 19.3 min-1
E) 0.0260 min-1
2
10
The rate constant of a first-order reaction is 3.68 x 10-2 s-1 at 150°C, and the activation
energy is 71 kJ/mol. What is the value of the rate constant at 170°C?
A) 9.2 x 10-2 s-1
B) 3.7 x 10-2 s-1
C) 2.49 s-1
D) 4.0 x 10-2 s-1
E) none of the above
11
In order to obtain the activation energy of a reaction using a graphical method,
__________ is plotted against _________, giving a straight line whose slope is equal
to __________.
A) k; T; -Ea
B) k; 1/T; -Ea
C) lnk; T; -Ea/R
D) k; 1/T; -Ea/R
E) lnk; 1/T; -Ea/R
12
Select the appropriate rate law for the elementary process shown below.
2A → B + C
A) Rate = k[2A]
B) Rate = k[A]
C) Rate = k[A]2
D) Rate = k[A]1/2
E) Rate = 2k[A]
13
The reaction
3ClO-(aq) → ClO3-(aq)
+ 2Cl-(aq) has been proposed to occur by the following mechanism.
ClO-(aq) + ClO-( aq)→ ClO2-( aq) + Cl-( aq) (slow)
ClO2-(aq) + ClO-(aq) → ClO3-(aq) + Cl-(aq) (fast
Which rate law is consistent with this mechanism?
A) rate = k[ClO-]
B) rate = k[ClO-]3
C) rate = k[ClO2-][ClO-]
D) rate = k[ClO-]2
E) rate = k[Cl-][ClO-]2
14
Consider the reaction:
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
A suggested mechanism for this reaction follows:
(1) NO(g) + NO(g) → N2O4(g) (slow)
(2) N2O4(g) + H2(g) → N2(g) + H2O2 (g) (fast)
(3) H2O2(g) + H2(g) → 2H2O(g) (fast)
Based on this mechanism, which, if any, of the following actions will not affect the
rate of the reaction?
3
A)
B)
C)
D)
E)
adding a catalyst
adding more NO(g)
adding more H2(g)
increasing the temperature
All of these will affect the rate of the reaction.
15
A catalyst speeds up a reaction by
A) increasing the number of high-energy molecules.
B) increasing the temperature of the molecules in the reaction.
C) increasing the number of collisions between molecules.
D) increasing the activation energy for the reaction.
E) providing a new reaction pathway for molecules.
16
Consider the reaction:
CH3Cl(aq) + OH-(aq) → CH3OH(aq) + Cl-(aq)
If the rate of appearance of CH3OH(aq) remains constant at 1.0 x 10-4 mol/(L·min),
and the initial concentrations of both reactants are 0.10 mol/L, how long will it take to
consume half of the reactants?
A) 10,000 min
B) 1,000 min
C) 500 min
D) 100 min
E) none of the above
17
Consider the reaction
2A + 2B + C → 2D + E
If the rate law for this reaction is Rate = k[A][B]2, what will be the effect on the rate if
the concentrations of A, B and C are all doubled at the same time?
A) The rate will increase by a factor of 2.
B) The rate will increase by a factor of 4.
C) The rate will increase by a factor of 6.
D) The rate will increase by a factor of 8.
E) More information is needed before this question can be answered.
18
Nitric oxide (NO) reacts with hydrogen (H2) according to the equation:
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
The following initial rates of reaction have been measured for the given reactant
concentrations.
Which of the following is the rate law (rate equation) for this reaction?
A) rate = k[NO]2 [H2]
4
B)
C)
D)
E)
rate = k[NO] [H2]2
rate = k[NO] [H2]4
rate = k[NO] [H2]
rate = k[NO]1/2 [H2]1/4
19
The following initial rate data were collected for the reaction:
2A + B → C + D
What is the value of the rate constant?
A) k = 1.42 x 10-2 s-1
B) k = 2.83 x 10-3 L mol-1 s-1
C) k = 1.42 L2 mol-2 s-1
D) k = 0.532 x 10-3 L2 mol-2 s-1
E) k = 4.26 x 10-1 L mol-1 s-1
20
A solution of sucrose in water has an initial concentration of 0.155 mol/L. The
sucrose is being converted to other sugars in a reaction which is first-order with
respect to the sucrose concentration. Exactly 30 minutes later, the sucrose
concentration has fallen to 0.131 mol/L. Calculate the value of the rate constant in s-1.
A) 9.3 x 10-5 s-1
B) 4.1 x 10-5 s-1
C) 5.6 x 10-3 s-1
D) 1.7 x 10-1 s-1
E) none of the above
21
The reaction A → products is first-order with respect to A. Which of the following
correctly describes a plot of rate data for this reaction?
A) [A] plotted vs time gives a straight line of negative slope.
B) [A] plotted vs time gives a straight line of positive slope.
C) ln[A] plotted vs time gives a straight line of positive slope.
D) ln[A] plotted vs time gives a straight line of negative slope.
E) 1/[A] plotted vs time gives a straight line of positive slope.
22
Tetrafluoroethene (C2F4) dimerizes at 300º C to form octafluorocyclobutane (cycloC4F8) according to the equation
2C2F4(g) → cyclo-C4F8(g)
The rate law for the reaction is:
Rate = (0.080 L mol-1 min-1)[C2F4]2
In an experiment where the initial concentration of tetrafluoroethylene is 0.10 mol/L,
what concentration remains after 700 min?
5
A)
B)
C)
D)
E)
8.0 X 10-3 mol/L
8.0 X 10-4 mol/L
2.8 X 10-3 mol/L
0.075 mol/L
0.015 mol/L
23
For the reaction A → products, the rate law is Rate = k[A]2. Starting with [A] = 0.100
mol/L, its concentration is found to be 0.0652 mol/L after 600. seconds. What is the
value of the rate constant?
A) 5.8 x 10-5 L . mol-1 .s-1
B) 7.1 x 10-4 L . mol-1 .s-1
C) 3.2 x 10-3 L . mol-1 .s-1
D) 8.9 x 10-3 L . mol-1 .s-1
E) none of the above
24
In an enzymatic fermentation, the initial concentration of sugar is 0.16 mol/L; after
10.0 hours the concentration is 0.080 mol/L; after 20.0 hours the concentration is
0.040 mol/L. What is the order of this reaction, and what is the rate constant?
A) zero order; 1.67 x 10-6 s-1
B) first order; 1.93 x 10-5 s-1
C) first order; 1.67 x 10-6 s-1
D) second order; 3.71 x 10-10 s-1
E) second order; 1.67 x 10-6 s-1
25
From the following data, estimate the activation energy for the gas-phase reaction
H2 + I2 → 2HI
A)
B)
C)
D)
E)
21.0 kJ/mol
2.10 x 104 kJ/mol
1.75 x 102 kJ/mol
9.00 x 102 kJ/mol
none of the above
26
A second-order rate constant is given by
k = (6.5 x 107 L·mol-1·s-1)e-13500 K/T
What is the the activation energy, Ea, for this reaction?
A) 135 kJ/mol
B) 56 kJ/mol
C) 112 kJ/mol
D) 162 kJ/mol
E) 782 kJ/mol
6
27
The reaction of ethylene (C2H4) with butadiene (C4H6) to form cyclohexene (C6H10)
has an activation energy (Ea) of 115 kJ/mol. The reverse reaction (decomposition of
cyclohexene to ethylene and butadiene) has an activation energy of 287 kJ/mol. What
is the heat of reaction, Δ Hrxn, for the forward reaction?
A) +115 kJ/mol
B) +287 kJ/mol
C) -287 kJ/mol
D) +172 kJ/mol
E) -172 kJ/mol
28
Consider the following mechanism for the oxidation of bromide ions by hydrogen
peroxide in aqueous acid solution.
(1) H+ + H2O2 → H3O2+ (rapid equilibrium)
(2) H3O2+ + Br- → HOBr + H2O (slow)
(3) HOBr + H+ + Br- → Br2 + H2O (fast)
What is the overall reaction equation for this process?
A) 2H+ + H2O2 + Br- + HOBr → H3O2+ + Br2 + H2O
B) H3O2+ + H+ + 2Br- → Br2 + 2H2O
C) 2H+ + 2Br- + H2O2 → Br2 + 2H2O
D) 2H3O2+ + 2Br- → H2O2 + Br2 + 2H2O
E) none of the above
29
The mechanism for the gas-phase reaction
2NO + Cl2 → 2NOCl
is suggested to be:
(1) NO + NO → N2O4 (slow)
(2) N2O4 + Cl2 → 2NOCl (fast)
Based on this mechanism, the rate law for the overall reaction is:
A) Rate = k [NO]
B) Rate = k [NO]2
C) Rate = k [NO2]2[Cl2]
D) Rate = k [Cl2]
E) Rate = k [NO2]2[Cl2]2
30
At elevated temperatures in the gas phase, cyclopropane reacts to form propene. The
rate of reaction is given by:
rate = Δ[propene]/Δt = k[cyclopropane].
Which one of the following actions is least likely to cause a change in the rate of this
reaction?
A) adding a catalyst
B) raising the temperature
C) doubling the initial amount of cyclopropane
D) halving the volume of the reaction vessel, but keeping the initial amount of
cyclopropane constant.
E) continuously removing propene as it is formed
7